function theme_primary_menu_links($menu = NULL) {
  $output = '';

  $pid = variable_get('menu_primary_menu', 0);
  if ($menu_tree = theme('nice_menu_tree', $pid, $menu)) {
    if ($menu_tree['content']) {
      $output .= '<ul class="nice-menu nice-menu-down" id="nice-menu-primary">'. $register . $menu_tree['content'] .'</ul>';
    }
  }

  return $output;
}